I have the same experience. My daughter is 18 months and recently her temper becomes bad. She normally goes to sleep at 11:00pm but in most of the times, she will awake at 11:30 to 12:00, sometimes 12:30 and cry in a crazy way. We have to take her in arms and do something to attract her in order to make her stop crying.
We have tried every possible thing to improve it, but nothing works for us. Music, environments, daytime schedules, foods, doctor visit....etc. everything that could help have already been done. My colleagues pray for her. My mother 拜神. However, she is extremely normal at daytime.
In the night before last night, my daughter cried from 2:00 to 5:00 pm.
Last night we went to bed at 4:30am. I can only sleep 2.5 hrs. This situation has been like this since 8 months ago. Sometimes it seems better, but sometimes worse.